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Old 15-05-2016, 14:17   #1
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Battery wiring question: 2 engines and genset

Hi guys!

I am about the rewire my electrical system on the boat (both AC & DC).

I have 2 engines and a genset.

I am planning to have 1 house bank
3 separate starter batteries

It is not good to have 2 engines charging the same battery bank.
How can I solve the problem?
I don't want to split the house battery bank into 2.

I found this diagram from Blue Sea Systems:


But I am not sure if an automatic charging relay is enough to save the alternator regulators from killing each other when both engines are running.

Please help me out!

Thank you
Bahia
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Old 15-05-2016, 14:21   #2
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Re: Battery wiring question: 2 engines and genset

It is fine. But I would not put an acr between the gen battery and rest. The gen alts are tiny. Just let it charge its own battery . Have a small onboard charger to maintain gen battery on shore. Or use agm gen battery if not planing to run for a while.

I think they have messed up the switch diagram. The gen one doesn't shut off the gen. Battery cable should be on battery post like all the others

Though i wouldn't follow that switching anyways. That is just weird.
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Old 15-05-2016, 14:27   #3
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Re: Battery wiring question: 2 engines and genset

Here's a question: wouldn't the regulator on one motor sense the charging current from the other and not activate the alternator?
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Old 15-05-2016, 14:44   #4
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Re: Battery wiring question: 2 engines and genset

if the batteries are at 100% and you remove all battery loads I have seen this happen. But if you at 100% then it doesn't matter as you don't need the charge. (Well the tach will stop if it's from alt, seen that)

If the batteries are not full then both will be charging. Or as soon as you add a decent load again
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Old 15-05-2016, 14:58   #5
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Re: Battery wiring question: 2 engines and genset

Hi!

The genset battery is independent and will remain independent.

Still being confused about 2 engines charging 1 house battery bank.
Loads of sources state that this is not right.
How can I eliminate any risks of potential failures?

Thanks again
Bahia
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Old 15-05-2016, 17:24   #6
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Re: Battery wiring question: 2 engines and genset

I have installed dual acrs feeding a house bank on hundreds of boats.

It is no different then having one engine + the AC charger off gen. Or one engine plus wind and solar. Everything charges one bank at same time.
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Old 15-05-2016, 22:27   #7
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Re: Battery wiring question: 2 engines and genset

Hi smac,

I have already bought Victron Cyrix CT acrs.
Are they suitable for this kinda setup?

Thanks
Bahia
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Old 16-05-2016, 09:04   #8
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Re: Battery wiring question: 2 engines and genset

consider installing a Sterling alternator/battery charger device. it senses and isolates the house batteries from the start batteries and makes sure they all receive the correct amount of current.
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Old 16-05-2016, 22:37   #9
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Re: Battery wiring question: 2 engines and genset

Quote:
Originally Posted by Bahia View Post

Still being confused about 2 engines charging 1 house battery bank.
Loads of sources state that this is not right.
How can I eliminate any risks of potential failures?

Thanks again
Bahia
There is no potential risk or failure. If the batteries are in bulk they will accept the total of the 2 alternator outputs - as long as they can accept that amount of current. One will reach its set point first - even if they have the same regulator settings - but by then the batteries are at about 85% SOC and accept less current from then until full.
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Old 16-05-2016, 22:41   #10
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Re: Battery wiring question: 2 engines and genset

Why a start battery for each engine? Better to parallel 2 batteries and use them to start both engines (if you already have the batteries) or if you don't just buy one good battery to start both.

With a house bank and a gen battery you already have enough redundancy. It also makes for a simpler charging system.
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Old 17-05-2016, 02:43   #11
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Re: Battery wiring question: 2 engines and genset

Quote:
Originally Posted by Bahia View Post
Hi guys!

I am about the rewire my electrical system on the boat (both AC & DC).

I have 2 engines and a genset.

I am planning to have 1 house bank
3 separate starter batteries
Hello, there's no need for 3 starter batteries which for 99% of the time are going to just sit there and do nothing. I would just use one and use the space for extra house batteries.

Starting an engine doesn't take much out of the battery so rewire the alternators to go to the house batteries and use the voltage sensitive relay to combine the house and starter banks. Wiring this way the relay won't carry alot of amps to charge the house bank. If the alternators are connected and can be isolated via the house battery switch then add some stranded relays to disable the ignitions for the engines - this way you won't start the engine without the alternators been connected to a battery.

I would also use a bus bars to reduce the amount of connections on the batteries.

Multiple alternators are okay to be connected together, batteries will only take the current they need. However if you have a small house bank and large amp alternators it may be better to wire one alternator (the smallest if different) to the start battery.

Let me know if a wiring diagram would help on my suggestion.
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